This invention relates generally to antennas capable of uniform signal radiation or reception throughout a hemispherically shaped space. More particularly, the invention relates to spherical antennas employing radial cavities and/or cylindrical cavities.
The use of antenna assemblies for both transmission and reception of radio signals is well known, and such antenna assemblies have taken many diverse dimensions and/or shapes to accomplish specific objectives. Among such antennas known in the art are those used in satellite vehicles launched in orbit around the earth to serve as active radio relay stations. Commonly, the satellite vehicles are spherically shaped and employ a radiant cavity or structures in the proximity of the diameter of the sphere. The satellite is then spin stabilized about an axis normal to the orbit so that the antenna is essentially equatorially positioned in the vehicle. Typically, the radiation pattern of these conventional antennas is rather directional and strongest in the plane of the active antenna element.
Antennas that are located near the surface of the earth which communicate with satellite vehicles have also taken on many different forms each suited for a particular application. The specific characteristics of an anetnna in a specific application not only dictate requisite electromagnetic radiation characteristics but also desirable physical properties. Isotropic antenna radiation coverage, that is a pattern of constant relative power or sensitivity in a defined space, minimizes the effect of antenna orientation upon communication. Small physical size, high structural strength, and low wind resistance are desirable properties for such an antenna which would not limit its adaptability to almost any mobile application.
A primary object of this invention is to provide an antenna having an essentially hemispherical signal radiation characteristic of substantially uniform signal gain.
A further object is to provide an antenna of sufficient compactness and rigidity compatible with mobile uses including a utility range from manpack to airborne applications.
Another object is to provide an antenna having a circular polarization characteristic over a wide angular range.
A still further object is to provide an antenna whose size is small and whose weight is low.
A still further object is to provide an antenna in accordance with the aforementioned objectives also capable of rather broadband radiation characteristics in two distinct frequency ranges.